The field of the invention is mufflers for internal combustion engines and the invention relates more specifically to mufflers for engines of the type commonly used on motorcycles. It is desirable to have an optimum amount of back pressure to optimize the efficiency of the the engine. The amount of back pressure also affects the noise, and the typical motorcycle muffler is designed to provide a compromise of backflow for a perceived average user. However, because motorcycle engines are often upgraded or altered with improved performance carburetors and other accessories, the preconceived amount of back pressure is often not equal to the optimum back pressure in any given situation.
It is, thus, beneficial to provide a muffler which has an adjustable amount of back pressure. One such design of muffler utilizes a plurality of disks inserted near the exit face thereof and the greater number of disks inserted, the lower the back pressure. Such system, however, is relatively cumbersome to adjust, and in the event the extra plates are misplaced, the adjustment feature is no longer available.